Propagation of repetitive alpha waves over the scalp in relation to subjective preferences for a flickering light

Abstract

Paired-comparison tests were performed to examine subjective preferences for a flickering light. Electroencephalograms were then recorded from seven electrodes (10–20 system) during presentations of the most and least preferred flickering-light conditions. As a way of investigating the flow of alpha waves on the scalp over both the left and right hemispheres in relation to subjective preference, the alpha waves were analyzed by means of the cross-correlation function (CCF). The maximum value of the CCF, |φ(τ)|_max, between the alpha waves measured at different electrodes and its delay time, τ_m, were analyzed. Results show that the most preferred flickering light has a significant larger |φ(τ)|_max than the least preferred flickering light, and that |φ(τ)|_max decreases with increasing distance between comparison (O₁ or O₂) and test electrodes. On the other hand, the delay time of the maximum value of the CCF, τ_m, increases with the distance between comparison and test electrodes.

Introduction

The efforts to describe important qualities of sound and light in terms of the processes of the auditory and visual pathways and brain has been brought to bear on the problem (Ando and Noson, 1997). If enough were known about how the auditory, the visual, and the central nervous systems modify the nerve impulses from the cochlea and retina, the design of concert halls and lighting, for example, could proceed according to guidelines derived from knowledge of these processes. Here, attempts to investigate for this purpose have been made through studies of electroencephalogram (EEG).

Techniques that are based on the autocorrelation function (ACF) and the cross-correlation function (CCF) have been developed to describe the nature of EEGs (Braizer and Casby, 1952, Barlow, 1961, McLachlan and Shaw, 1965, Liske et al., 1967, Hoovey et al., 1972). A technique based on the CCF has been developed for identifying, in humans, dynamic spatiotemporal electrical patterns of the brain during purposive behaviors (Gevins et al., 1981, Gevins et al., 1983). The interhemispheric relationships during sleep have been investigated by using the CCF (Barcaro et al., 1986). The persistence of oscillations in the ACF has been used for identifying seizure activity and for being of clinical utility for characterizing electroconvulsive therapy seizures (Krystal et al., 1996). The ACF is used to determine characteristics over time, that is, the degree of persistence of a signal. The CCF is used to examine mutual relationships for signals detected at two electrode sites, the presence of common components, and transmission times.

The oscillatory components of EEG have been related to perception and cognitive processing (Singer and Gray, 1995). Visual stimulation and cognitive activity suppress alpha waves while increasing the power of the high frequency beta and gamma bands (Pfurtscheller and Klimesch, 1990). Temporal spectral evolution analysis showed that the decrease in alpha band and the increase in beta band during visual spatial attention (Marrufo et al., 2001). Alpha waves, which have the longest period of the EEG forms seen in subjects who are awake, are also thought to indicate pleasant and comfortable feelings. The differentiation of basic emotions, i.e. intention, anxiety, aggression, sadness, and joy by means of EEG-coherences has been discussed extensively (Hinrichs and Machleidt, 1992). Intention, aggression and joy are mainly characterized by an increase in alpha-coherence, whereas a decrease is seen for anxiety and sorrow. Changes in the EEG that appeared with mental processes of a higher order have been analyzed by using coherence analysis (Petsche, 1996). Acts of creative visual thinking were characterized by increased alpha-coherence between occipital and frontopolar electrode sites. The relationship between subjective preferences and alpha waves on the scalp has been studied by using the ACF (Ando and Chen, 1996, Chen and Ando, 1996, Chen et al., 1997, Mouri et al., 2000, Soeta et al., 2002a). In these studies, the effective duration of the envelope of the normalized ACF, τ_e, of EEG alpha waves was analyzed. The results showed that the τ_e value of alpha waves is longer when the subject is presented with preferred conditions. The spread of alpha waves over the scalp has also been studied by using the CCF (Inoye et al., 1983, Nishio and Ando, 1996, Chen, 1997). A propagation of alpha waves from right to left that corresponds to the change in the magnitude of the interaural CCF has been observed (Nishio and Ando, 1996).

We have recently found that the ACF factor, τ_e, of alpha waves has a strong correspondence with subjective preference for a flickering light (Soeta et al., 2002a, Soeta et al., 2002b). ACF analysis concentrates on the intra-channel correspondences in the time domain. Numerous studies have reported relationships between EEG coherence and mental processes. Coherence analysis concentrates on inter-channel correspondences in the frequency domain. Accordingly, it is logical to assume that subjective preferences for visual stimuli are reflected in both the intra-channel and inter-channel relations between EEG alpha waves in the time domain. These relationships between subjective preference and alpha waves over the scalp were investigated by using the CCF. We chose subjective preference as a primitive response that would lead the individual away from inappropriate environments and toward desirable ones and relate to aesthetics, affect and cognition (Kaplan, 1987). A flickering light varying the period and the mean luminance was used because it is simple and basic.